1. Field of the Invention
The present invention relates to a quantitative feeding apparatus for various kinds of liquid reagents, which may be used for measuring a dissolved oxygen concentration of water, water hardness, a water pH value, and the like, as well as a quantitative feeding apparatus or quantitative injection apparatus for various kinds of chemicals in the medical field. More specifically, the invention relates to a liquid feeding apparatus of a cassette system which allows liquid cassettes to be freely fitted to and removed from the apparatus.
2. Description of the Prior Art
Conventionally, in various types of water examinations, roller pumping or tube pumping devices have been widely used as quantitative feeding devices for various kinds of liquid reagents. In the medical field, pumping devices have also been used as quantitative feeding or quantitative injection devices for various kinds of chemicals. With regard to these pumping devices, various techniques in which an elastic tube is provided in a removable cassette have been proposed, and are disclosed, for example, in U.S. Pat. Nos. 4,537,561 and 4,886,431.
In these prior-art examples, in either case, only the elastic tube is provided in a cassette so as to be freely fittable and removable. During quantitative feeding or quantitative injection, while the elastic tube, disposed along an arc-shaped guide portion serving as a tube receiver, is pressed and pinched by a multiplicity of press rollers, the press rollers are rotationally moved on circular tracks so as to sequentially move the pressed, clogged points of the elastic tube along the rotational direction of the drive shaft. In this way, a reagent or chemicals or the like within the tube (i.e., a liquid) is sucked and fed. In this arrangement, so that the liquid within the elastic tube is measured and fed by two adjacent press rollers, at least one press roller is in contact with the arc-shaped guide portion while clogging the elastic tube. As a result, at least one press roller is normally kept in contact with the arc-shaped guide portion while clogging the elastic tube, so that the elastic tube remains deformed flat during a rest of the feeding operation. Then, when the rest of feeding operation is prolonged, the restoring power of the elastic tube is weakened for resuming the feeding operation. Moreover, the elastic tube yields fatigue deterioration such that an accurate sucking and feeding operation cannot be maintained over a long period.
Also in the aforementioned prior-art examples, since only the elastic tube is provided in a removable cassette, only one kind of liquid can be fed in actual use. As a result, in order to feed other kinds of liquids, it would be necessary to reattach or reconnect one end of the elastic tube to reservoirs (liquid tanks) for other kinds of liquids, or to replace the liquid within the liquid reservoir, where it also becomes necessary to clean the elastic tube for feeding other kinds of liquids. Because of these factors, the foregoing prior-art arrangements exhibit considerably poor versatility, such that general versatility would require very complex operation. In particular, reagents or chemicals in these cases would involve deterioration problems in that contact with air may cause them to change or deteriorate in properties and effects. Further, when replacing liquid, care must be taken to avoid the invasion of air bubbles.
Furthermore, in various types of water examinations and in the medical field, there are some cases where two or more kinds of liquids are mixed and fed. In such a case, with the above prior-art examples, there is a need to premix several kinds of liquids and store the mixture in the premixed state. As a result, retaining the effects of such mixed liquids for a long period becomes a serious issue.